1. Field of the Invention
This invention relates to a control system for an internal combustion engine, and more particularly to a control system that controls desired torque of an internal combustion engine installed on an automotive vehicle during acceleration of the engine.
2. Description of the Prior Art
Conventionally, a control system of this kind was proposed e.g. in Japanese Laid-Open Patent Publication (Kokai) No. 5-133257, in which a required torque T is calculated based on a sensed engine rotational speed and a sensed stepping amount of an accelerator pedal, and then a state of acceleration/deceleration of the engine is determined from the difference between the present value Ti and the immediately preceding value Tixe2x88x921 of the required torque T calculated. If it is determined that the engine is not being accelerated, i.e. does not require acceleration, a desired torque Txe2x80x2 is set to the present value Ti of the required torque (Txe2x80x2=Ti), whereas if it is determined that the engine is being accelerated, i.e. requires acceleration, the required torque T is smoothed by using a smoothing value DTSET for calculation of the desired torque Txe2x80x2. During acceleration of the engine from a fuel-cut state, the smoothing value DTSET is set to and held at a smaller constant reference value DTSET0 until a predetermined time period has elapsed after the engine started to be accelerated, whereas after the lapse of the predetermined time period, the smoothing value DTSET is switched and set to a larger constant reference value DTSET1. The desired torque Txe2x80x2 is calculated by adding the smoothing value set as above to the immediately preceding value Tixe2x88x921 of the required torque (Txe2x80x2=Tixe2x88x921+DTSET).
The desired torque Txe2x80x2 calculated as above is converted to a desired throttle valve opening, and then the throttle valve is controlled such that its opening becomes equal to the desired throttle valve opening. As described above, in the above control system, at an initial stage of acceleration of the engine starting from the fuel-cut state, the required torque is smoothed to a larger degree to thereby ensure drivability, and thereafter, the degree of smoothing is reduced to thereby ensure acceleration response of the engine.
However, in the above conventional control system, when it is determined that the engine is being accelerated, the required torque T is smoothed by using the smoothing value DTSET which is a fixed value all through the acceleration, and hence it is impossible to obtain an acceleration response of the engine excellent enough to meet a driver""s demand, which causes a sense of tardiness in acceleration especially at the initial stage of the acceleration at which the degree of smoothing of the required torque is large. Further, in the control system, during acceleration of the engine, the desired torque Txe2x80x2 is set to the sum of the immediately preceding required torque value Tixe2x88x921 and the smoothing value DTSET (Txe2x80x2=Tixe2x88x921+DTSET), and except during the acceleration, it is set to the present required torque value Ti (Txe2x80x2=Ti), which means that, basically, the required torque T determined directly from the engine rotational speed and the stepping amount of the accelerator pedal serves as a basic value of the desired torque Txe2x80x2. For this reason, the basic value varies in a manner oversensitive even to slight changes in the driver""s operation of the accelerator pedal, and the desired torque Txe2x80x2 is readily changed accordingly. Therefore, the behavior of the vehicle is liable to become unstable, and hence, drivability is degraded particularly when the accelerator pedal is repeatedly fully stepped on and released.
It is an object of the invention to provide a control system for an internal combustion engine for an automotive vehicle, which is capable of setting a desired torque appropriately during acceleration of the engine, thereby ensuring an excellent response of the engine and drivability of the vehicle.
To attain the above object, the present invention provides a control system for an internal combustion engine, for setting a desired torque in response to operating conditions of the engine and controlling torque based on the set desired torque.
The control system according to the invention is characterized by comprising:
rotational speed-detecting means for detecting an engine rotational speed;
accelerator position-detecting means for detecting an accelerator position;
required torque-calculating means for calculating a required torque, based on results of detection by the rotational speed-detecting means and the accelerator position-detecting means;
required torque-smoothing means for smoothing the required torque calculated by the required torque-calculating means;
acceleration-determining means for comparing a present value of the required torque calculated by the required torque-calculating means at a present time with the smoothed required torque smoothed by the required torque-smoothing means, to thereby determine whether or not the engine is being accelerated;
acceleration assist amount-calculating means for calculating an acceleration assist amount, based on a difference value between the present value of the required torque and the smoothed required torque, when the acceleration-determining means determines that the engine is being accelerated; and
desired torque-setting means for adding the acceleration assist amount to the smoothed required torque to thereby set the desired torque.
According to this control system, the required torque-calculating means calculates the required torque based on the sensed engine rotational speed and accelerator position, and the required torque-smoothing means smoothes the required torque calculated by the required torque-calculating means, to thereby determine the smoothed required torque. Further, the acceleration-determining means compares the present value of the required torque calculated by the required torque-calculating means with the smoothed required torque smoothed by the required torque-smoothing means, to thereby determine whether or not the engine is being accelerated. Then, when it is determined that the engine is being accelerated, the acceleration assist amount-calculating means calculates the acceleration assist amount, based on the difference value between the present value of the required torque and the smoothed required torque. Further, the desired torque-setting means adds the acceleration assist amount to the smoothed required torque to thereby set the desired torque.
As described above, in the control system according to the invention, the present value of the required torque and the smoothed required torque are compared with each other, whereby it is determined whether the engine is being accelerated. Further, the acceleration assist amount is calculated based on the difference value between the present value of the required torque and the smoothed required torque, and then the acceleration assist amount is added to the smoothed required torque, whereby the desired torque is set. Therefore, the acceleration assist amount properly determined according to the degree of acceleration of the engine can be added to the required torque while reflecting the driver""s demand for acceleration in real time, so that it is possible to ensure an excellent acceleration response of the engine and thereby eliminate tardiness in acceleration of the vehicle. Further, in place of the required torque calculated directly from the engine rotational speed and the accelerator position, the smoothed required torque is employed as a basic value of the desired torque to which the acceleration assist amount is to be added, so that the basic value of the desired torque is prevented from varying in a manner oversensitive to changes in the driver""s operation of the accelerator, which makes it possible to stabilize the behavior of the vehicle and hence ensure excellent drivability.
Preferably, the acceleration assist amount-calculating means calculates the acceleration assist amount such that the acceleration assist amount is progressively increased during a start of the acceleration mode and progressively reduced during an end of the acceleration mode.
According to this preferred embodiment, the acceleration assist amount is progressively increased during the start of the acceleration mode of the engine and progressively reduced during the end of the same, which enables acceleration of the engine to be smoothly started and ended without causing sharp changes in the desired torque. Therefore, even when the accelerator pedal is fully stepped on and released repeatedly, it is possible to stabilize the behavior of the vehicle and hence ensure excellent drivability.
More preferably, the engine includes a transmission, and the control system further comprises change gear ratio-detecting means for detecting a change gear ratio of the transmission of the engine, the acceleration assist amount-calculating means calculating the acceleration assist amount such that the acceleration assist amount is larger as the change gear ratio detected by the change gear ratio-detecting means is smaller.
In general, torque required during acceleration of the engine is larger as the change gear ratio (reduction gear ratio) is smaller. Therefore, according to the above preferred embodiment, since the acceleration assist amount is calculated such that it becomes larger as the selected change gear ratio is smaller, it is possible to obtain an excellent acceleration response adapted to the selected change gear ratio.
Preferably, the smoothing by the required torque-smoothing means is carried out by calculating an average value of a predetermined number of values of the required torque calculated up to the present time.
Preferably, the control system further comprises start assist amount-calculating means for calculating a start assist amount based on said engine rotational speed and said accelerator position, and said desired torque-setting means adds said acceleration assist amount and said start assist amount to said smoothed required torque to thereby set said desired torque.
The above and other objects, features, and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings.